async异步函数的执行顺序

async function async1(){
    console.log('async1 start') //2
    await async2()
    //await async2()后面的内容可以看做是callback里得内容即是异步
    //类似eventloop,settimeout
    //Promise.resolve().then(()=>{console.log(async1 end)})
    console.log('async1 end') //5
}

async function async2(){
    console.log('async2') //3
}

console.log('script start') //1
async1()
console.log('script end') //4

 变体

async function async1(){
    console.log('async1 start') //2
    await async2()
    //后面都是异步回调callback的内容
        console.log('async1 end') //4
        await async3()
            console.log('async2 end') //6
}

async function async2(){
    console.log('async2') //3
}

async function async3(){
    console.log('async3') //5
}

console.log('script start') //1
async1()
console.log('script end') //4

 异步函数 返回的是一个promise  内部await相当于then,await后面的是异步回调内容